The goal of the proposed project is to obtain an understanding of the structure, and its relationship to the function, of proteins/glycoproteins associated with the plasma membrane, which mediate the uptake of amino acids and cholesterol-rich low density lipo-protein (LDL) in mammalian cells. Gamma glutamyl transpeptidase enzyme, localized in the plasma membrane of the mammalian cells, has been hypothesized to play an important role in mediating the uptake of amino acids. The present studies are aimed to substantiate this hypothesis, utilizing gamma-glutamyl transpeptidase reconstituted liposomes containing entrapped glutathione as a model membrane system. This proteoliposomal system has been found to exhibit the uptake of L-leucine. It is proposed to study the uptake of various amino acids in this system in an attempt to determine the relationship between the amino acid acceptor specificity of the enzyme to the transport of amino acids mediated by it. In addition to describing the conditions conducive to reassembly of gamma-GTPase in phospholipid vesicles, studies on the effect of phospholipid composition on the disposition of gamma-GTPase in liposomes may shed light on the membrane protein assembly processes in the natural membranes. Studies will carried out to understand the mechanism of amino acid translocation mediated by gamma-GTPase in the model membrane system. Another membrane associated protein/glycoprotein whose physico-chemical structure we propose to investigate is the low density lipoprotein (LDL) membrane receptor, which is involved in the binding and uptake of LDL in non-hepatic cells. A novel approach utilizing cleavable heterobifunctional (photoaffinity) ligand coupled to LDL will be used to covalently cross-link the membrane receptor in lymphocytes and skin fibroblast cells. Attempts will be made to employ this probe for the purification of LDL receptors from lymphocyte cell membranes. These studies would provide an insight into the mechanism of uptake of LDL in normal cells and molecular understanding of the defect of LDL receptor observed in the cells of familial hypercholesterolemic individuals.